The present invention relates to a piston internal-combustion engine having a control system for controlling the stroke sequence of the engine-operating process as a function of operating parameters, and to a process for controlling and automatically controlling the operating mode of a piston internal-combustion with a variable sequence of strokes as a function of operating parameters.
DE-A-196 31 799 describes a piston internal-combustion engine and a process in which a piston internal-combustion engine has six working strokes and a variable valve timing is operated by four strokes-during a warm-up phase and by six strokes after the operating temperature has been reached. The number of strokes can only be varied between a four and six stroke operation, with a pushing of the combustion products out of the combustion space of the cylinder in all cases taking place during the fourth stroke. The fifth stroke is a working stroke. At its start, water is sprayed into the cylinder in order to generate water vapor in the cylinder which is still hot from the preceding combustion. The pressure of this water vapor moves the piston further along. The sixth stroke is used for pushing out the water vapor.
DE-A 33 17 128 discloses an internal-combustion engine having a six-stroke cycle, in which the push-out stroke for pushing out the combustion products is always the sixth stroke.
Both known concepts have in common that the number of strokes of the internal-combustion engine is either fixed from the beginning or can be varied between only two values. The combustion products are pushed out of the cylinder no later than during the sixth stroke, irrespective of whether they still contain combustible parts or residual oxygen or not. As a result, a portion of the energy which can still be utilized in the cylinder is lost. Because power losses occur with each charge cycle as the result of valve movements and flows, premature charge cycles have a negative effect on the efficiency of the internal-combustion engine.
Modern directly injecting NFZ diesel engines reach an efficiency which is comparatively high for internal-combustion engines with effective efficiencies of up to 45% in the full-load range. In the partial load range, the efficiency is reduced to values of about 30% and below. This is the result of the lower pressure level and temperature level of the combustion, the high charge cycle losses caused by the pressure gradient from the exhaust gas side to the intake side and the high proportion of mechanical losses. Because internal-combustion engines in vehicles are operated in the partial load range for a considerable portion of their operation, this represents a serious disadvantage.
Measures which endeavor to obtain an improvement of the internal efficiency by raising the internal-combustion pressure level and the temperature level, however, result in a rise of the nitrogen oxide (NO.sub.x) emissions. Furthermore, the capability to be mechanically and thermally stressed with respect to the peak pressure and the internal-combustion temperature in the full-load operation represents the limit for the above-mentioned measures furthering the partial load operation.